Quote:
Originally Posted by drgondog
Let's take one more pass at this.
Assume max TO power, brakes on, zero velocity. I say that is the condition of Max Thrust Available for the system at that altitude.
The system does not accelerate, no drag forces are experienced and the force retarding the thrust is the friction on the wheels with the brakes creating the torque to keep the wheels from rotating.
Release brakes, Same Max Thrust Available.
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At the beginning speed is zero (V=0) so the formula:
T = (n*W)/V
can't be used but as example the one for V=0 in the Hamilton Standard book (above formula for V>0).
Quote:
Originally Posted by drgondog
The Max Thrust available exceeds the thrust required and the system accelerates until the speed is sufficient to create enough lift to overcome weight. Same Max Thrust but the a/c is airborne and continues to accelerate.
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This is mostly true for the jets but not for the propeller planes. We can assume that power remains fairly constant (save the RAM and altitude effects), but thrust will vary according to formula for V>0.
Quote:
Originally Posted by drgondog
Drag forces increase as the system accelerates until the drag forces equal the Max Thrust Available... at that point the system has reached maximum velocity for that system with that Max Thrust available. It is in equilibrium.
At no time did Max Thrust available change from V=0 through V=Vmax for that weight condition.
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This part is only partially true, the plane will reach equilibrium but while the velocity increase, the thrust at constant power will decrease.
Quote:
Originally Posted by drgondog
Add 500 pounds of fuel.
Everything is the same for this System B except that induced drag increases throughout the profile in comparison to the lighter weight system
MAX THRUST available for the System B is the same as it was in the lighter weight system, but the aircraft will achieve equilibrium at a lower speed because the Thrust required to attain an equal velocity of the lighter weight system is insufficient to overcome the increased induced drag due to the heavier weight system.
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This part is also only partially true because thrust increase when the speed decrease.
The power is constant, however, the thrust depends on speed.
IMHO the main problem here is that you have apparently played with the jets.
Quote:
Originally Posted by drgondog
So, Harri - by your use of the conversion of Jet Thrust to THP conversion equations do you believe that Thrust just increased in the example above by virtue of the reduction in velocity as described in System A above?
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It's not just my use of this very basic formula but also Hamilton Standard, Hoerner, NACA, NASA, RAE... you name it. Below is quote from Hoerner.
Note that the speed value is in foots per second and 1200 is amount of power in hp.